Mechanical properties test speed effects

The measurement of mechanical properties is a major part of the domain of characterisation. The tensile test is the key procedure, and this in turn is linked with the various tests to measure fracture toughness... crudely speaking, the capacity to withstand the weakening effects of defects. Elaborate test procedures have been developed to examine resistance to high-speed impact of projectiles, a property of civil (birdstrike on aircraft) as well as military importance. Another kind of lest is needed to measure the elastic moduli in different directions of an anisotropic crystal this is, for instance, vital for the proper exploitation of quartz crystal slices in quartz watches. 

The low-speed mechanical properties of polymer blends have been frequently used to discriminate between different formulations or methods of preparation. These tests have been often described in the literature. Examples of the results can be found in the references listed in Table 12.9. Measurements of tensile stress-strain behavior of polymer blends is essential [Borders et al., 1946 Satake, 1970 Holden et al., 1969 Charrier and Ranchouse, 1971]. The mbber-modified polymer absorbs considerably more energy, thus higher extension to break can be achieved. By contrast, an addition of rigid resin to ductile polymer enhances the modulus and the heat deflection temperature. These effects are best determined measuring the stress-strain dependence. 

This chapter presents an overview of properties and performance of polymer blends. It is structured into nine sections dealing with aspects required for assessing the performance of a polymer blend. These are mechanical properties comprising of both low-speed and high-speed popularly studied properties chemical and solvent effects thermal and thermodynamic properties flammability electrical, optical, and sound transmission properties and some special test methods which assumed prominence recently because of their utility. 

Li et al. [37] showed that the tensile properties of sisal fibres are not uniform along their length. Parameters such as fibre length, test speed, gauge length, fibre age or temperature were all found to have effects on the mechanical properties of sisal and sun-hemp fibres. Most of these effects are explained by the internal structure of... 

Tensile and notch-tensile tests of AISI 304 were conducted at the four test temperatures listed above. In addition, two other variables, strain rate and thermal cycling, were introduced. The strain rates employed were those resulting from crosshead speeds of 0.005, 0.02 and 0.2 in. per min. at each test temperature. To determine the effect of thermal cycling on mechanical properties of AISI 304 in the absence of spontaneous martensitic transformation, one half of all the specimens were subjected to temperature cycling between 300° and 76°K (holding at 76°K) for a period of one year [2]. 

Some studies with filled and unfilled rigid PVC were made in our laboratory to describe the effect of chalk as additional stabilizer. A suspension PVC (K-value 70) with an organotin stabilizer (2 phr) and lubricants (1.8 phr) was used as the experimental material. A part of this compound was filled with a stearic acid coated calcium carbonate (10 phr) as an additional component. The PVC powder and the additives were mixed at a high speed in an intensive mixer. The received dry blends were pelletized by extrusion to get a better dispersion of the additives in the polymer material. Finally, the granulates were processed by injection molding to test specimens for measurements of mechanical properties. 

Rapid strain-induced crystallization has been associated with the outstanding mechanical properties characteristic of crosslinked NR compared to its synthetic analogue, i.e. crosslinked IR. This may be due in part to a reinforcing effect of strain-induced crystals on the properties of NR as a filler or physical crosslinking junctions. In fact, tensile and tear strengths of crosslinked NR are practically higher than those of crosslinked IR, at the high-speed limit of the tear test." Therefore, it is important to control the rate of crystallization, in order to control the mechanical properties of not only NR itself, but also the NR blends. 

The effect of the absorbed humidity on the mechanical properties was characterized by tensile testing performed at 25°C at a crosshead speed of 100 mm/min on a Lloyd Instruments material testing machine, finked to a microcomputer for data acquisition and analysis. For each case, the result reported is an average over five specimens. 

For cubic symmetry materials, three independent elastic properties that are orientation dependent are required to describe the mechanical behavior of the material. This anisotropy effect increases significantly the number of the nonzero elements in the FE stiffness matrix leading to alteration in the calculated stress components and the wave speed. In order to test these anisotropy effects, we plot the wave profiles of three different orientations and compare it with the isotropic behavior with a loading axis in the [001] directions as shown in Fig 8. We observed that under the same loading condition, the peak stress of [111] and [Oil] orientations are slightly higher than those of the [001] which is lower that that of isotropic material. Furthermore, wave speed varies moderately with orientation with the fastest moving wave in the [ 111 ] followed by [011 ], isotropic medium and [001 ] respectively. 

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